This invention is drawn to the field of materials science, and more particularly, to a novel method for improving the soft magnetic properties of amorphous alloy toroids.
Amorphous metallic alloys may be formed by a variety of techniques including melt-quenching a molten stream onto a rapidly cooled substrate, electro-deposition and splat quenching among others. The resulting amorphous alloys may be binary, tertiary, quarternary, etc. compositions having elements typically selected from the group consisting of the transition metals with the metalloids.
A variety of techniques are known for tailoring the soft magnetic properties of such materials. Graham, Jr. et al, U.S. Pat. No. 4,053,331, issued Oct. 11, 1977, incorporated herein by reference, controls the soft magnetic properties of amorphous metallic alloy ribbons by applying elastic tensile loading. Egami et al, U.S. Pat. No. 4,053,332, issued Oct. 11, 1977, incorporated herein by reference, controls the soft magnetic properties of amorphous alloy ribbons by applying elastic tensile loading to a ribbon passed between two rollers to obtain a reduction in thickness. The rolling tends to reduce the unloaded remanence and improve the load versus remanence range sensitivity. Egami et al, U.S. Pat. No. 4,053,333, issued Oct. 11, 1977, incorporated herein by reference, provides a method for enhancing the residual soft magnetic properities of amorphous alloy ribbons which comprises the steps of subjecting an amorphous alloy ribbon to a predetermined tensile stress, heating the stressed ribbon to a predetermined temperature, maintaining the stressed ribbon in the heated state for a predetermined duration, cooling the ribbon after the predetermined duration and removing the stress. Becker et al, U.S. Pat. No. 4,116,728, issued Sept. 26, 1978, incorporated herein by reference, provides a method for tailoring the residual soft magnetic properties of amorphous alloys which comprises the steps of heating an amorphous alloy to a temperature sufficient to relieve stress in the alloy and less than that required to initiate crystallization, and cooling the alloy in the presence of a directed magnetic field.
It has been observed, however, that when the known techniques are applied to amorphous alloys wrapped in a toroidal configuration the soft magnetic properties show marked deterioration. The observed deterioration in soft magnetic properties of amorphous alloy toroids is believed to be the effect of a strain-induced anisotropy which is caused by the winding stresses introduced by the toroidal geometry and which are "frozen-in" by the action of a suitable stress-relief anneal. Reference in this connection may be had to an article entitled "Strain Induced Anisotropy In Amorphous Alloys And The Effect Of Toroid Diameter On Magnetic Properties", appearing in IEEE Transactions Magnetics, Vol. MAG-15, p 1939 (1979), by Luborsky et al and to an article entitled "Amorphous Materials--A New Class of Soft Magnetic Alloys", appearing in Journal of Magnetism and Magnetic Materials, Volume 19, p. 130 (1980), by Luborsky et al both of which are incorporated herein by reference. The former article shows that the soft magnetic properties of amorphous alloy toroids improve with increasing toroid diameter. It is further known that it is desirable to increase the packing fraction of a toroid in order to minimize its volume to provide maximum flux density. Thus, it is desirable to provide a method for improving the soft magnetic properties of amorphous alloy toroids without sacrificing the packing fraction.